1. Field of the Invention
The present invention relates in general to tube fittings and, more particularly, to metal tube fittings of the type suitable for use in air brakes.
2. Description of the Prior Art
Tube fittings for air brakes are generally formed of metal such as brass. Metal is required because of the more rigorous and extreme conditions encountered by the tube fitting and the requirement of higher reliability. Brass is preferred over steel since it is necessary that n rust be present in the air brake lines which provide pneumatic power to the brakes of the vehicles on which they are installed.
Generally the tubes which are connected to air brake fittings are made of nylon strengthened by a braided sheath and covered with a nylon exterior coating. Such tubes are capable of providing the strength, flexibility and wear resistance needed for this extreme condition usage. Metal fittings, more particularly brass fittings, are well suited to connect to this type of tubing.
Among the extreme conditions encountered by the air brake tube fittings are extreme high and extreme low temperatures. Vibration and higher tensile loads are also commonly encountered. It is difficult to provide a fitting which has a convenient means of coupling with tubing which, nevertheless, is reliable in these difficult conditions.
Although brass air brake tube fittings have been in use for many years, only relatively recently have such tube fittings been developed which utilize the convenient push-in method of coupling the tube fitting. By push-in tube fitting it is meant that the only requirement for coupling and sealing a tube in connection with the tube fitting is that the tube be pushed into the tube fitting. It is not necessary to tighten nuts or screws or the like.
It is especially difficult to create such a push-in tube fitting which has the capability of releasing the tube if it is desired to change the tube. Changing the tubing is required, for example, if the tubing becomes cut or begins to wear or is otherwise likely to leak.
Because of the requirement of high reliability, it is even more difficult to provide such a releasable, push-in, air brake tube fitting which is simple in its construction so as to be more reliable. Simplicity of construction is especially critical due to the dirt and vibration which would damage or destroy more complex designs.